[Python-checkins] bpo-32308: Replace empty matches adjacent to a previous non-empty match in re.sub(). (#4846)

Thu Jan 4 04:06:16 EST 2018

https://github.com/python/cpython/commit/fbb490fd2f38bd817d99c20c05121ad0168a38ee
commit: fbb490fd2f38bd817d99c20c05121ad0168a38ee
branch: master
author: Serhiy Storchaka <storchaka at gmail.com>
committer: GitHub <noreply at github.com>
date: 2018年01月04日T11:06:13+02:00
summary:
bpo-32308: Replace empty matches adjacent to a previous non-empty match in re.sub(). (#4846)
files:
A Misc/NEWS.d/next/Library/2017-12-13-20-31-30.bpo-32308.CUbsb2.rst
M Doc/howto/regex.rst
M Doc/library/re.rst
M Doc/whatsnew/3.7.rst
M Lib/test/test_re.py
M Modules/_sre.c

diff --git a/Doc/howto/regex.rst b/Doc/howto/regex.rst
index fa8c6939408..87a6b1aba59 100644
--- a/Doc/howto/regex.rst
+++ b/Doc/howto/regex.rst
@@ -1140,12 +1140,12 @@ new string value and the number of replacements that were performed::
 >>> p.subn('colour', 'no colours at all')
 ('no colours at all', 0)
 
-Empty matches are replaced only when they're not adjacent to a previous match.
+Empty matches are replaced only when they're not adjacent to a previous empty match.
 ::
 
 >>> p = re.compile('x*')
 >>> p.sub('-', 'abxd')
- '-a-b-d-'
+ '-a-b--d-'
 
 If *replacement* is a string, any backslash escapes in it are processed. That
 is, ``\n`` is converted to a single newline character, ``\r`` is converted to a
diff --git a/Doc/library/re.rst b/Doc/library/re.rst
index dae1d7ea10a..9b175f4e967 100644
--- a/Doc/library/re.rst
+++ b/Doc/library/re.rst
@@ -708,12 +708,15 @@ form.
 That way, separator components are always found at the same relative
 indices within the result list.
 
- The pattern can match empty strings. ::
+ Empty matches for the pattern split the string only when not adjacent
+ to a previous empty match.
 
 >>> re.split(r'\b', 'Words, words, words.')
 ['', 'Words', ', ', 'words', ', ', 'words', '.']
+ >>> re.split(r'\W*', '...words...')
+ ['', '', 'w', 'o', 'r', 'd', 's', '', '']
 >>> re.split(r'(\W*)', '...words...')
- ['', '...', 'w', '', 'o', '', 'r', '', 'd', '', 's', '...', '']
+ ['', '...', '', '', 'w', '', 'o', '', 'r', '', 'd', '', 's', '...', '', '', '']
 
 .. versionchanged:: 3.1
 Added the optional flags argument.
@@ -778,8 +781,8 @@ form.
 The optional argument *count* is the maximum number of pattern occurrences to be
 replaced; *count* must be a non-negative integer. If omitted or zero, all
 occurrences will be replaced. Empty matches for the pattern are replaced only
- when not adjacent to a previous match, so ``sub('x*', '-', 'abc')`` returns
- ``'-a-b-c-'``.
+ when not adjacent to a previous empty match, so ``sub('x*', '-', 'abxd')`` returns
+ ``'-a-b--d-'``.
 
 In string-type *repl* arguments, in addition to the character escapes and
 backreferences described above,
@@ -805,6 +808,9 @@ form.
 Unknown escapes in *repl* consisting of ``'\'`` and an ASCII letter
 now are errors.
 
+ Empty matches for the pattern are replaced when adjacent to a previous
+ non-empty match.
+
 
 .. function:: subn(pattern, repl, string, count=0, flags=0)
 
diff --git a/Doc/whatsnew/3.7.rst b/Doc/whatsnew/3.7.rst
index 1924881219a..1311e9e2016 100644
--- a/Doc/whatsnew/3.7.rst
+++ b/Doc/whatsnew/3.7.rst
@@ -881,8 +881,9 @@ Changes in the Python API
 * The result of splitting a string on a :mod:`regular expression <re>`
 that could match an empty string has been changed. For example
 splitting on ``r'\s*'`` will now split not only on whitespaces as it
- did previously, but also between any pair of non-whitespace
- characters. The previous behavior can be restored by changing the pattern
+ did previously, but also on empty strings before all non-whitespace
+ characters and just before the end of the string.
+ The previous behavior can be restored by changing the pattern
 to ``r'\s+'``. A :exc:`FutureWarning` was emitted for such patterns since
 Python 3.5.
 
@@ -893,7 +894,13 @@ Changes in the Python API
 positions 2--3. To match only blank lines, the pattern should be rewritten
 as ``r'(?m)^[^\S\n]*$'``.
 
- (Contributed by Serhiy Storchaka in :issue:`25054`.)
+ :func:`re.sub()` now replaces empty matches adjacent to a previous
+ non-empty match. For example ``re.sub('x*', '-', 'abxd')`` returns now
+ ``'-a-b--d-'`` instead of ``'-a-b--d-'`` (the first minus between 'b' and
+ 'd' replaces 'x', and the second minus replaces an empty string between
+ 'x' and 'd').
+
+ (Contributed by Serhiy Storchaka in :issue:`25054` and :issue:`32308`.)
 
 * :class:`tracemalloc.Traceback` frames are now sorted from oldest to most
 recent to be more consistent with :mod:`traceback`.
diff --git a/Lib/test/test_re.py b/Lib/test/test_re.py
index aaed3d893aa..9fed4bef880 100644
--- a/Lib/test/test_re.py
+++ b/Lib/test/test_re.py
@@ -213,11 +213,6 @@ def test_bug_114660(self):
 self.assertEqual(re.sub(r'(\S)\s+(\S)', r'1円 2円', 'hello there'),
 'hello there')
 
- def test_bug_462270(self):
- # Test for empty sub() behaviour, see SF bug #462270
- self.assertEqual(re.sub('x*', '-', 'abxd'), '-a-b-d-')
- self.assertEqual(re.sub('x+', '-', 'abxd'), 'ab-d')
-
 def test_symbolic_groups(self):
 re.compile(r'(?P<a>x)(?P=a)(?(a)y)')
 re.compile(r'(?P<a1>x)(?P=a1)(?(a1)y)')
@@ -331,10 +326,10 @@ def test_re_split(self):
 ['', 'a', '', '', 'c'])
 
 for sep, expected in [
- (':*', ['', 'a', 'b', 'c', '']),
- ('(?::*)', ['', 'a', 'b', 'c', '']),
- ('(:*)', ['', ':', 'a', ':', 'b', '::', 'c', '', '']),
- ('(:)*', ['', ':', 'a', ':', 'b', ':', 'c', None, '']),
+ (':*', ['', '', 'a', '', 'b', '', 'c', '']),
+ ('(?::*)', ['', '', 'a', '', 'b', '', 'c', '']),
+ ('(:*)', ['', ':', '', '', 'a', ':', '', '', 'b', '::', '', '', 'c', '', '']),
+ ('(:)*', ['', ':', '', None, 'a', ':', '', None, 'b', ':', '', None, 'c', None, '']),
 ]:
 with self.subTest(sep=sep):
 self.assertTypedEqual(re.split(sep, ':a:b::c'), expected)
@@ -357,7 +352,7 @@ def test_qualified_re_split(self):
 self.assertEqual(re.split("(:+)", ":a:b::c", maxsplit=2),
 ['', ':', 'a', ':', 'b::c'])
 self.assertEqual(re.split("(:*)", ":a:b::c", maxsplit=2),
- ['', ':', 'a', ':', 'b::c'])
+ ['', ':', '', '', 'a:b::c'])
 
 def test_re_findall(self):
 self.assertEqual(re.findall(":+", "abc"), [])
@@ -1753,13 +1748,13 @@ def test_match_repr(self):
 def test_zerowidth(self):
 # Issues 852532, 1647489, 3262, 25054.
 self.assertEqual(re.split(r"\b", "a::bc"), ['', 'a', '::', 'bc', ''])
- self.assertEqual(re.split(r"\b|:+", "a::bc"), ['', 'a', '', 'bc', ''])
- self.assertEqual(re.split(r"(?<!\w)(?=\w)|:+", "a::bc"), ['', 'a', 'bc'])
+ self.assertEqual(re.split(r"\b|:+", "a::bc"), ['', 'a', '', '', 'bc', ''])
+ self.assertEqual(re.split(r"(?<!\w)(?=\w)|:+", "a::bc"), ['', 'a', '', 'bc'])
 self.assertEqual(re.split(r"(?<=\w)(?!\w)|:+", "a::bc"), ['a', '', 'bc', ''])
 
 self.assertEqual(re.sub(r"\b", "-", "a::bc"), '-a-::-bc-')
- self.assertEqual(re.sub(r"\b|:+", "-", "a::bc"), '-a--bc-')
- self.assertEqual(re.sub(r"(\b|:+)", r"[1円]", "a::bc"), '[]a[][::]bc[]')
+ self.assertEqual(re.sub(r"\b|:+", "-", "a::bc"), '-a---bc-')
+ self.assertEqual(re.sub(r"(\b|:+)", r"[1円]", "a::bc"), '[]a[][::][]bc[]')
 
 self.assertEqual(re.findall(r"\b|:+", "a::bc"), ['', '', '::', '', ''])
 self.assertEqual(re.findall(r"\b|\w+", "a::bc"),
diff --git a/Misc/NEWS.d/next/Library/2017-12-13-20-31-30.bpo-32308.CUbsb2.rst b/Misc/NEWS.d/next/Library/2017-12-13-20-31-30.bpo-32308.CUbsb2.rst
new file mode 100644
index 00000000000..d760d6089ba
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2017-12-13-20-31-30.bpo-32308.CUbsb2.rst
@@ -0,0 +1,2 @@
+:func:`re.sub()` now replaces empty matches adjacent to a previous non-empty
+match.
diff --git a/Modules/_sre.c b/Modules/_sre.c
index 68fc523c251..b6be6f6ffa6 100644
--- a/Modules/_sre.c
+++ b/Modules/_sre.c
@@ -955,7 +955,7 @@ _sre_SRE_Pattern_split_impl(PatternObject *self, PyObject *string,
 }
 
 n = n + 1;
- state.must_advance = 1;
+ state.must_advance = (state.ptr == state.start);
 last = state.start = state.ptr;
 
 }
@@ -1109,7 +1109,7 @@ pattern_subx(PatternObject* self, PyObject* ptemplate, PyObject* string,
 
 i = e;
 n = n + 1;
- state.must_advance = 1;
+ state.must_advance = (state.ptr == state.start);
 state.start = state.ptr;
 }
 
